1. Field of the Invention
The present invention relates to a heat-sensitive recording material, specifically, a high image-quality heat-sensitive recording material suitable for medical recording media and the like.
2. Description of the Related Art
In recent years, the heat-sensitive recording method has been developing in various fields since the method has advantages, for example, as-the following: (1) no development is necessary, (2) if the support of heat-sensitive recording material is paper, the paper is like a general paper, (3) operation is easy, (4) color density of the resultant image is high, (5) a recorder is simple, highly reliable and inexpensive, (6) no noise occurs at the time of recording, and (7) no maintenance is needed. The use of the heat-sensitive recording method has been expanding over the field of facsimile and printer, the field of label such POS, and other fields.
As heat-sensitive recording materials used in the heat-sensitive recording, a material using reaction between an electron-donating colorless dye and an electron-accepting compound, a material using reaction between a diazo compound and a coupler, and the like materials have been widely known.
In recent years, there is a need for developing heat-sensitive recording materials having a heat-sensitive recording layer on a transparent support, an image being able to be recorded on the heat-sensitive recording material directly by means of a thermal head, so that a recorded image can be projected through an overhead projector or the image can be observed directly on a light table. Attention has been paid, in particular, to transparent heat-sensitive recording materials as materials for forming images for medical diagnosis.
Although the transparency of such transparent heat-sensitive recording materials themselves is good, the materials have problems that when images are recorded on the materials with a heat-sensitive recording device such as a thermal printer, sticking or noise easily occurs. In particular, when transparent heat-sensitive recording materials are used for medical use, a high transmission density is required for the materials; therefore, thermal energy applied by means of a thermal head becomes large so that problems such as sticking, noise in the recording, and the abrasion of the thermal head become serious. Thus, a protective layer consisting mainly of a pigment and a binder is provided on the heat-sensitive recording layer in order to suppress sticking and noise. Besides the protective layer, at least one selected from gas blocking layers, undercoat layers, ultraviolet ray filter layers, antireflection layers and other layers can also be provided.
In order to provide these layers on a support, there are known a method of forming the respective layers successively over the support, and a method of forming all the layers simultaneously by multilayer coating in an extruding die manner.
The multilayer coating method is preferable since an underlying layer does not influence a layer on the underlying layer and no liquid repellent mark is generated. However, when the coating speed is increased in order to make the efficiency of the production high, the dried surface becomes uneven and the state of the surface tends to deteriorate.
In particular, when a transparent heat-sensitive recording material is used to produce an image for medical diagnosis, precise diagnosis cannot be attained if details of formed image are not clear. Deterioration of surface state of a heat-sensitive recording material exerts a bad influence on formed image.
In order to solve the above-mentioned problems, a heat-sensitive recording material comprising a specific acetylene glycol derivative is suggested, and surface deficiency is largely reduced (for example, Japanese Patent Application Laid-Open (JP-A) No. 2002-283730).
It has been requested that in a heat-sensitive recording material, in particular, in a heat-sensitive recording material applied to medical diagnosis, surface deficiency should be further reduced so as to form high-quality images.